1. Field of the Invention
The present invention relates to a film forming method comprising: moving a substrate and nozzle with respect to each other; dropping solution onto the substrate from a solution discharge nozzle; and forming a liquid film of the solution on the substrate.
2. Description of the Related Art
To use a spin coating method in a lithography process and interlayer film formation, most of the solution dropped onto a substrate is discharged off the substrate, and a film is formed with the remaining several percent of the solution. Therefore, there is much waste, and the environment is adversely affected. Moreover, there has been a problem that turbulence is generated in an outer peripheral portion of a square substrate or a circular substrate having a large diameter of 12 inches or more, making the film thickness nonuniform in that portion.
As a method of uniformly coating the whole surface of the substrate without wasting in Jpn. Pat. Appln. KOKAI Publication No. 2-220428, a method is described which comprises: dropping resist from a large number of nozzles arranged in one row; and spraying a gas or solution onto a film forming surface from behind the nozzles to obtain a uniform film. Further, in Jpn. Pat. Appln. KOKAI Publication No. 6-151295, a large number of spray ports are disposed in a bar; and the resist is dropped onto the substrate from the ports to obtain a uniform film. Furthermore, in Jpn. Pat. Appln. KOKAI Publication No. 7-321001, a method is described comprising: using a spray head in which a large number of jet holes are formed to spray the resist; and moving the head with respect to the substrate to coat the substrate. In all of these coating apparatuses, a plurality of dropping or spray nozzles are transversely arranged in a row, so as to scan the nozzles along the substrate surface and a the uniform film. In addition to these coating methods, there is a method using one solution discharge nozzle, and scanning the nozzle to form a liquid film. This method has a problem that the treatment time per substrate depends on the operation method of the nozzles, and the amount of solution used becomes enormous.
As an apparatus for solving the problem, in Jpn. Pat. Appln. KOKAI Publication No. 9-92134, a method is disclosed which comprises: reciprocating/moving the solution discharge nozzle over the substrate to drop the solution onto the substrate. The method further comprises: stopping liquid supply in each terminal end of the reciprocating/moving on the substrate; and re-supplying the solution in a start point to form the coating film. However, the solution amount supplied onto the substrate slightly differs due to uneven liquid supply caused by stoppage and restart of liquid supply at the terminal end and start point, and a problem has occurred that film thickness uniformities of the liquid film and solid film formed from the liquid film are deteriorated.
On the other hand, in Jpn. Pat. Appln. KOKAI Publication Nos. 2000-77307, 2000-77326, 2000-79366, 2000-188251, 2001-148338, 2001-168021, 2001-170546, 2001-176781, 2001-176786, 2001-232250, and 2001-232269, a method is disclosed comprising: maintaining the discharge of the solution even in a turn-back portion in the reciprocating movement of the solution discharge nozzle; and supplying a coating film in which a film thickness distribution at an edge vicinity (the vicinity of turn-back of reciprocating movement) is not deteriorated. However, in the coating apparatus described in these publications, a distance between the solution discharge nozzle and substrate is not considered. Depending on the discharge speed from the solution discharge nozzle, surface tension of the solution, and distance between the solution discharge nozzle and substrate, in a process of spread of liquid flow before the solution reaches the substrate, liquid drops are produced by the surface tension of the liquid, and the liquid drops which have reached the substrate are sputtered, causing a problem of mist or vapor.
Moreover, in the above-described forming method in the liquid film, in each region of the substrate surface to be treated, because of differences of physical properties, discharge pressure of the nozzle, further variations in discharge amount of the solution, or turbulence of air currents at the coating time, the film thickness of the liquid film does not become uniform, and sometimes varies over the whole surface of the substrate. When a solvent in the liquid film is vaporized in this state, a film of a solid content (=solid film) is formed on the substrate with low flatness in accordance with the film thickness distribution of the liquid film.
Moreover, even when the liquid film is formed in a excellent flatness state, when a drying process is thereafter executed so as to vaporize the solvent, aggregation occurs toward the middle portion of the substrate. In this manner, the solid content moves with the movement of the liquid film in a transverse direction, and a difference in film thickness is generated in the movement direction.
When a such photo resist film which is formed using the such method is subjected to exposure and development processes to form a pattern, a critical dimension (CD) error is generated in the pattern. In a process in which this pattern is used as a mask to subject a lower layer film (e.g.: insulating film, and conductive wiring film) to etching processing, the CD error is further enlarged. This was an effect of reaucing the yield.
As disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2001-237179, with respect to the variation in thickness of the liquid film, there has heretofore been a method comprising: forming the liquid film; subsequently exposing the film to a solvent vapor to promote fluidity of the solution; and performing a so-called leveling treatment so that the surface of the liquid film is flatted by the surface tension.
However, in the prior-art leveling treatment, the solvent is unnecessarily supplied to the surface of the liquid film, and the film thickness is uneven. Inclination is generated in the film thickness of the liquid film (e.g., peripheral edge) by an inadequate condition.
Additionally, a manufacturing process of the semiconductor apparatus comprises: coating the substrate surface with a resist solution in which resist materials such as a resin, dissolution inhibitor (dissolution inhibitor group), and acid generating material (acid generation group) are dissolved in organic solvent (ethyl lactate, etc.) to form the liquid film; and subsequently evaporating the solvent in the liquid film to form the resist film. The resist film formed on the substrate is exposed to light, then bake-treated, cooled, and developed to form a resist pattern.
Some of the resist patterns formed as described above have a problem that the upper part of the resist pattern is rounded. Since the upper surface of the resist film is exposed to a developing liquid for a long time, the upper part becomes rounded. To solve this problem, a layer containing many dissolution inhibitor can be formed in the surface layer.
However, to form the layer containing many dissolution inhibitor in the surface layer, a prior art method has to comprise: coating the substrate with a first resist solution film; baking and forming a first resist film; coating the first resist film with a second resist solution film using a resist solution which containing the dissolution inhibitor more than the resist solution used in forming the first resist film; and baking and forming the second resist film. In this method, two resist films have to be separately formed, which lengthens manufacturing time.
As a prior-art method of forming the coating film on the substrate, there is a method comprising: relatively moving a discharge nozzle which discharges a given amount of solution on the substrate; discharging the solution over the whole surface of the substrate to form a liquid film; and thereafter evaporating the solvent by an appropriate dry method to form the film. In this method, a solution which has a small solid content and has a low viscosity in a range of about 0.001 Pa·s to 0.010 Pa·s (1 cp to 10 cp) is used. When the liquid film is formed on a substrate having a stepped portion in this coating method, the formed liquid film is fluidized by gravity, and a concave/convex portion is smoothed. A difference is generated in the thickness of the finally prepared coated film, that is, the film thickness of the concave portion increases and that of the convex portion decreases. As a result, there is a problem that a film having a uniform thickness cannot be formed on the substrate surface.